The term "essentially plate-shaped workpieces" wherein is intended to signify parts for electroplating which extend primarily within one plane, i.e., are planar in nature, but which can also have parts or sections projecting out of this "plane." A preferred embodiment is printed circuit boards, but the invention is not limited to the treatment of these latter. [German Patent] DE-PS 37 26 571 provides, in a shielding and positioning frame for printed circuit boards in immersion plating plants, a mask, designed like the ridge of a roof and guided by means of lateral tabs into the vertically running slots of a holder. The "ridge" of this "roof" is oriented downward. The mask's initial position is on the surface of the bath. The printed circuit board to be treated is lowered by its bottom edge into the "interior of the roof" and takes the mask downward along with it during the immersion process. This mask prevents "burn-on," i.e., undesirable additional metallization deposits in the lower marginal area of the board. This prior-art device has several disadvantages. The mask must be pressed downward by the printed circuit board. These boards are often very thin and, therefore, unable to transmit the forces necessary for this downward pressing without suffering damage. In such cases, the sensitive printed circuit boards bow outward under the effects of the pressing forces, which can damage the boards and produce differences in the thickness of the deposits on their convex and concave sides. Moreover, the DE-PS 37 26 571 device is limited to masking the lower area of the workpieces to be treated. Thus, it is suitable for treating printed circuit boards of different heights. However, its applicability in this case is limited to only one vertically-positioned printed circuit board at a time, and this board must be suspended by its top edge using means such as retaining clamps.
[Japanese Patent] JP 55-145 199 A, in Patent Abstracts of Japan, Sect. C, Vol. 5 (1981), No. 16 (C-41), sets forth a masking device whose structure corresponds in principle to that of DE-PS 3 726 571; hence, the foregoing commentary applies to it as well.
As for [Japanese Patent] JP 62-116 799 A, in Patent Abstracts of Japan, Sect. C, Vol. 11 (1987), No. 332 (C-455), it sets forth a device that includes a frame interposed between the anode and the piece to be treated, forming a window through which the field lines pass. The height of this window cannot be changed. Only the width of the window can be changed, by means of shielding plates. These plates can be moved inward from the frame's vertical struts according to the degree of shielding desired. As will be seen from the embodiments presented below, the problem and solution dealt with by the present invention cannot be gleaned from this reference document.
DE-OS [German Patent Application, (Unexamined)] 30 27 751 concerns a device for electroplating substrates, primarily by the attachment of the substrate, or of multiple substrates, to an upper contact bar. The level of the contact bar can be adjusted by means of a screw, but this must be performed manually for each level, specifically by loosening the adjustment, placing the contact bar in the proper position and relocking it in said position. Such manipulations are complicated. Also provided are masks for the partial masking of field lines; a disadvantage, however, is that these masks cannot be adapted to the individual workpiece as regards their masking action. Instead, a special mask must be provided for each workpiece shape and size.